Effect of Cathode–Anode distance and electrical resistivity on macrocell corrosion currents and cathodic response in cases of chloride induced corrosion in reinforced concrete structures

Abstract

When dealing with macrocell corrosion, it is crucial to consider the geometry and size of the structure, including the mobilizable cathode–anode distance, which is the maximum distance where passive reinforcement bars exchange current with corroding active sites. An application of the mobilizable cathode–anode distance is the corrosion of submerged regions of reinforced concrete structures where very high local anodic current densities were reported with no visual manifestation making this type of corrosion very dangerous. One possible explanation for these observations is that active steel (anode) bars in the submerged region could be coupled with a cathodic aerated zone located far away from the anode. This paper aims to study the influence of cathode–anode distance on the macrocell current. Experimental investigations were carried out on a 10 m long reinforced beam consisting of 20 segments of rebars: an anode where corrosion was initiated with chloride diffusion, and 19 identical cathodes. Different electrical connections were made between cathodes and corrosion currents were measured in order to test the impact of the cathode–anode distance on the evolution of corrosion current and the attenuation of the cathodic reaction in relation to the distance between anode and cathode. The experimental campaign was supported by numerical simulations, which confirmed the experimental results and tested the impact of electrical resistivity on the mobilizable cathode–anode distance. By connecting the anode to each cathode alone, it was found that macrocell corrosion current could be provided by cathode bars at large distances from the anode, the distance being dependent on the electrical resistivity of the structure. It was also found that, when all the cathodes were connected to the anode, the closest bar received the highest proportion of the total current, which increased with electrical resistivity, whereas the most distant bars received very limited amounts of current.